State and federal lawmakers also attended the event, held at a monument built in 1968, the first created on public land outside of Armenia.
During the Armenian Genocide from 1915 to 1923, some 1.5 million Armenians were killed by the Turkish government. Present-day Turkey disputes that the deaths should be termed a genocide and the U.S. government has been reluctant to use the term because of its NATO alliance with Turkey.
Some SoCal lawmakers at the Montebello event noted that a congressional resolution aims to give official U.S. recognition to the genocide.
The Montebello event was held in advance of Tuesday's worldwide commemoration of Armenian Genocide Remembrance Day.
In Los Angeles, thousands of people are expected to take part in the annual March for Justice, marching from Pan Pacific Park to the Turkish consulate.